Rifts emerge over why Arabian cyclones are strengthening

Rasha Dewedar in SciDev.net: People living in countries around the Arabian Sea have been exposed to tropical cyclones that have been growing in strength since 1997, and hitting the area earlier than usual — but scientists are still debating what is driving these changes. A study published in Nature last month (20 September) challenges previous conclusions that the stronger cyclones are being driven by man-made pollution, such as aerosol and sulphate emissions.

Instead, it claims, the stronger cyclones are caused by an earlier onset of the Asian summer monsoon, which in turn may be driven by natural variation or man-made warming. But the authors of the original paper, published in Nature in November 2011, reject the new findings and maintain that pollution is the fundamental cause.

Over the past 60 years, the Arabian Sea has been exposed to huge growth in emissions from the Indian subcontinent. The 2011 study, led by Amato Evan, an assistant professor at the Scripps Institution of Oceanography, United States, attributed the intensification of tropical cyclones since 1997 to this simultaneous upward trend in black carbon and sulphate emissions.

But Bin Wang, chair of the meteorology department at the University of Hawaii's International Pacific Research Center, United States, and collaborators in China, instead attribute the increase to the early onset of the Asian summer monsoon....

You might expect to see a storm with near-perfect symmetry and a well-defined eye hoovering over the warm waters of the Caribbean or in the South Pacific, but Tropical Cyclone Gonu showed up in an unusual place. On June 4, 2007, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this image, Tropical Cyclone Gonu was approaching the northeastern shore of Oman, a region better known for hot desert conditions. From NASA